The present invention relates to a fuel conditioning process for internal combustion engines of motor vehicles.
The improvement of fuel properties has positive effects on the cold-start performance, the exhaust-gas emission as well as the combustion noises of the internal combustion engine of a motor vehicle. Thus, for example, a Diesel fuel having a high cetane number brings about a reduction of the hydrocarbon and carbon-dioxide emissions as well as a reduction of the detrimental engine knock.
The cetane number of the Diesel fuel can be increased, for example, by ignition improvers. Ignition improvers that have proven efficient include additives, in particular, alkyl nitrates such as isopropyl nitrate, amyl nitrate, cyclohexyl nitrate or octyl nitrate as well as organic nitrites, nitro compounds or peroxides.
Known from Word Patent Application WO 79/00487 A12 and Japanese Patent 60 169 660 are methods for improving the fuel quality by introducing oxygen into fuel tanks.
U.S. Pat. No. 4,469,904 describes a process for selectively forming nitro compounds. In the process, organic carboxylic acids having from two to ten hydrocarbon atoms are contacted, at temperatures above 200° C. and pressures between 1 and 10 bars in a homogeneous gas phase, with nitrogen dioxide (NO2) or nitric acid (HNO3) in pure form, respectively, or in the presence of oxygen and/or water. A similar process for selectively nitrating aldehydes and ketones is disclosed in U.S. Pat. Nos. 4,524,226 and 4,517,393. The disclosed processes have the disadvantage that a lot of energy is required due to the elevated temperature and the increased pressure.